Method and system for conformal imaging vibrometry

ABSTRACT

Systems and methods for conformal imaging vibrometry capable of real-time measurements of the dynamic motions of any arbitrary two-dimensional or three-dimensional structure. The disclosed systems and methods are able to fully characterize the dynamic behavior of an object of any arbitrary geometry. The test object is illuminated with multiple laser beams whose directions conform to the local normal axis of the surface. The approach enables high-speed vibration imaging of whole-body dynamics of arbitrarily shaped structures in real-time, with no multiplexed data capture or synthesized motion reconstruction, as is currently practiced. By measuring the object&#39;s vibrations simultaneously at multiple points, the disclosed systems and methods are able to reproduce the structural behavior under operational conditions, which can then be spectrally decomposed to determine the modal, complex modal and transient nature of the true structural dynamics.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119(e)

This application claims the benefit and priority of U.S. ProvisionalPatent Application No. 61/713,040, entitled “METHOD AND APPARATUS FORCONFORMAL IMAGING VIBROMETRY,” filed on Oct. 12, 2012, the entirecontents and disclosures of which are hereby incorporated by referenceherein.

STATEMENT REGARDING GOVERNMENT RIGHTS

This invention was made with Government support under Contract Nos.N68335-11-C-0268, W31P4Q-11-C-0061, and W15P7T-13-C-A408, all awarded bythe Army Contracting Command Office—APG on behalf of the DefenseAdvanced Research Projects Agency (“DARPA”), and the Naval Air WarfareCenter Aircraft Division (“NAVAIR”). The Government has certain rightsin this invention.

BACKGROUND

1. Field of the Invention

The present invention relates generally to optics and more particularly,to conformal fiber-optics vibrometry for real-time full-fieldmeasurement of the displacement and vibration of arbitrarily-shapedsurfaces wherein the measurements are acquired by a conformalfiber-optics vibrometer array.

2. Description of the Related Art

A laser Doppler vibrometer (“LDV”) is essentially a laser interferometerdesigned specifically for remote, non-contact measurement of solid bodydynamic displacement, velocity, and other physical parameters ofinterest using homodyne or heterodyne demodulation techniques. Laserinterferometers include those broadly categorized as Michelson,Mach-Zehnder, Fabry-Perot, Sagnac, and Fizzeau. Interferometers commonlyemploy heterodyne detection techniques in which the frequency of thereference channel is offset from that of the signal channel. Theseinterferometers can be bulk-optic or hybrid bulk, fiber-opticsinterferometers.

Recently, all-fiber and hybrid bulk, fiber-optics interferometers havebeen developed using, for example, a varied combination of fibercouplers, isolators, circulators, polarizers, phase and intensitymodulators, fiber amplifiers, Bragg gratings, DFB laser diodes andwavelength-tunable fiber lasers. Thus, such fiber-optics technology isincreasingly being employed with LDVs to provide a convenient andflexible non-contact method to measure displacement and vibration of aremote surface at a point on the structure illuminated by a single laserbeam.

Currently, the global dynamics of an extended structure can only bedetermined by numerical (modal) analyses of data taken with a singlepoint sensor, such as an accelerometer or LDV which thus has to besequentially moved or scanned across the surface as the data aremeasured point by point. In traditional modal analyses, the frequencyresponse function of the structure (FRF), which is the ratio of outputresponse to input excitation, is determined at a number of separatelocations; thus, additional means are required to measure the inputforce such as an attached accelerometer or secondary referencevibrometer. However, there are limitations with traditional modalanalyses. For example, traditional modal analyses assume that (i) theinput excitation can be accurately measured, which may be difficult orimpossible in operational environments, (ii) the excitation andstructural response is repeatable and largely insensitive toenvironmental factors for the duration of the measurement, and (iii) thestructural dynamics are linear and time invariant (i.e. the principal ofmodal superposition is applicable).

Traditional modal analysis methods thus use a roving accelerometer inconjunction with fixed point impact (or vice versa), or swept sineexcitation or using non-contact laser vibrometry, such as a single-beamLDV. However, there are limitations with such approaches. For example,with a single beam LDV, characterization of the motion of an extendedarea of the structure relies on the use of XY scanning galvanometermirrors to reposition the laser beam over a grid of points on thesurface. The inference of global structural dynamic behavior is furthersubject to additional restrictive assumptions concerning the actualstructural behavior between sequentially scanned measurements.

In addition to the limitation of the restrictive assumptions implicit intraditional modal analyses, point measurements performed sequentiallyrequire application of repetitive stimulus for each point measurement,making this approach slow and unsuitable for the study of many systemdynamics or diagnostic problems which entail transient, non-repetitive,complex (i.e., travelling wave) effects, or any combinations thereof.Additionally, accurate recovery of the surface velocity is predicated onthe assumption that the measurement beam is substantially perpendicularto the surface. Where the incident beam makes an angle with the surface,the velocity estimate is in error by an amount proportional to thecosine of the angle which the beam makes with the surface normal.Another limitation of the current state-of-the-art LDV is its inabilityto measure the vibratory motion of structures comprising convoluted ornon-planar shapes, in particular where these are sufficiently small,reflective and/or delicate structures, such as micro-electromechanicalsensors (MEMS).

Recently, various designs for simultaneous multiple point LDVmeasurements on a structure at multiple locations have been proposed.However, such designs have the following limitations. They are notcapable of vibration imaging where “imaging” is taken to imply asufficient number of simultaneous measurement points to resolve thesmallest scale spatial vibrations of interest over a two-dimensional(“2D”) area. Implicit in the term “imaging vibrometry” is the assumptionthat each individual sensor or pixel measures the surface motion atrates exceeding the highest temporal frequencies of interest and thatthe density of the sensor array likewise exceeds the maximum spatialvibration frequency of interest. Thus, such designs do not provide animaging capability but instead employ, for example, a linear vibrometerarray in conjunction with mechanical rotation or scanning to acquire 2Ddata. Such approaches are thus susceptible to the same limitations ofsingle point scanning systems as detailed previously.

The aforementioned current state-of-the-art LDV includes, for example,(i) U.S. Pat. No. 8,446,575, entitled “Imaging Doppler velocimeter withdownward heterodyning in the optical domain,” (ii) U.S. Pat. No.7,193,720, entitled “Optical vibration imager,” (iii) U.S. Pat. No.7,116,426, entitled “Multi-beam heterodyne laser Doppler vibrometer,”(iv) U.S. Pat. No. 7,961,362, entitled “Method and apparatus for phasecorrection in a scanned beam imager,” and (v) PCT ApplicationPublication No. WO2002063237 A2, entitled “Interferometer.”

The current state-of-the-art LDVs attempt to address the limitations ofsingle beam measurements by providing a limited extension of LDV tospatially distributed measurements, but such approaches are not capableof vibration imaging and, in addition, are only applicable to planar orsubstantially planar surfaces and structures. Thus, the currentstate-of-the-art LDV fails to provide simultaneous measurements of thereal-time, full-field vibrometry motion of (i) structures with arbitrarygeometry, and, in particular, structures with curved surfaces such ascircular, cylindrical, spherical, or arbitrary curved two-dimensional orthree-dimensional surfaces, and (ii) structures which exhibit rapid,abrupt or discontinuous variations of surface curvature. Additionalexemplary structures include spherical, cylindrical and multi-facetedmicro-scale MEMS, convoluted turbine blades, leading edges of aerospacecontrol surfaces, and composite components employed in aerospaceapplications, such as thruster nozzles and nose cones. Therefore, thereis a need to address the foregoing limitations.

The present invention addresses the foregoing limitations by introducinga conformal imaging vibrometer (“CIV”) that extends real-time imagingvibrometry to any structural geometry of practical interest which is notamenable to measurement by current state-of-the-art laser vibrometersemploying a fixed line of sight.

SUMMARY OF THE INVENTION

The present invention aims to address the above-cited limitations incurrent state-of-the-art LDV by providing the ability to fullycharacterize the dynamic behavior of an object of any arbitrarygeometry, deploying a laser beam array tailored to the specificstructural geometry of interest (planar, circular, cylindrical,spherical or an arbitrary curved/warped 2D or 3D surface). For thepurpose of characterization, the object is illuminated with multiplelaser beams whose directions conform to the local normal axis of thesurface. This approach enables high-speed vibration imaging ofwhole-body dynamics of arbitrarily shaped structures in real-time, withno multiplexed data capture or synthesized motion reconstruction, as iscurrently practiced. By measuring the object's vibrations simultaneouslyat multiple points, the CIV is able to reproduce the structural behaviorunder operational conditions, which can then be spectrally decomposed todetermine the modal, complex modal and transient nature of the truestructural dynamics. The speed at which these measurements can be madepermits a wide range of further characterization tests. For example, theeffect of pressure and temperature variations on the object's dynamicscan be studied in real-time, where previously these parameters had to beheld or assumed constant throughout the measurement process. The CIVuses heterodyne interferometry, in which the velocity of the vibratingsurface is encoded in the Doppler sidebands of a frequency modulatedcarrier. The microprocessor recovers the displacement (or velocity) databy demodulating the measured, digitized signals to yield the localsurface displacement (or velocity) time histories, while the full dataset provides an animated display of the real-time surface deformation(or velocity) of the sample under transient (or, more generally,arbitrary) stimulus.

The contents of this summary section are provided only as a simplifiedintroduction to the invention, and are not intended to be used to limitthe scope of the appended claims. The present disclosure has beendescribed above in terms of presently preferred embodiments so that anunderstanding of the present disclosure can be conveyed. However, thereare other embodiments not specifically described herein for which thepresent disclosure is applicable. Therefore, the present disclosureshould not be seen as limited to the forms shown, which should beconsidered illustrative rather than restrictive.

An exemplary embodiment of the present invention's system for conformalimaging vibrometry capable of real-time measurements of the dynamicmotions of any arbitrary two-dimensional or three-dimensional structurecomprises a conformal beam illumination scheme configured for conformalimaging vibrometry of real-time dynamic behavior of a structure havingan arbitrary geometry, wherein the conformal beam illumination schemehas a fiber array and a plurality of conformal illuminating probes; amulti-channel interferometer, wherein the multi-channel interferometeris a multi-channel heterodyne interferometer, wherein the multi-channelheterodyne interferometer is an all-fiber multi-channel heterodyneinterferometer having a laser source, an optical isolator, a firstfiber-optics splitter configured to split a laser beam emitted from thelaser source into an object beam and a reference beam, a modulator, asecond fiber-optics splitter configured to split the object beam, athird fiber-optics splitter configured to split the reference beam, aplurality of fiber-optics circulators, a plurality of fiber-opticsre-combiners, and a plurality of receivers configured for receivingsignals from the plurality of fiber-optics re-combiners; a multi-channelreceiver array; and a computer having a display, a multi-channeldigitizer, and a microprocessor configured for digital signal processingand data analysis. Additionally, at least one conformal illuminatingprobe has a terminal end with (a) a bare fiber angle polished to anyangle from 8 degrees to 45 degrees, (b) a mirrored right-anglemicro-prism, or (c) a microlens.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a polarizing maintaining (PD) fiber array, a fiber ferrule, aflat-field lens, and a quarter-waveplate; a multi-channelinterferometer, wherein the multi-channel interferometer is amulti-channel heterodyne interferometer, wherein the multi-channelheterodyne interferometer is an all-fiber multi-channel heterodyneinterferometer having a laser source, an optical isolator, a firstfiber-optics splitter configured to split a laser beam emitted from thelaser source into an object beam and a reference beam, a modulator, asecond fiber-optics splitter configured to split the object beam, athird fiber-optics splitter configured to split the reference beam, aplurality of fiber-optics circulators, a plurality of fiber-opticsre-combiners, and a plurality of receivers configured for receivingsignals from the plurality of fiber-optics re-combiners; a multi-channelreceiver array; and a computer having a display, a multi-channeldigitizer, and a microprocessor configured for digital signal processingand data analysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a single mode (SM) fiber array, a fiber ferrule, a flat-fieldlens, and a Faraday rotator; a multi-channel interferometer, wherein themulti-channel interferometer is a multi-channel heterodyneinterferometer, wherein the multi-channel heterodyne interferometer isan all-fiber multi-channel heterodyne interferometer having a lasersource, an optical isolator, a first fiber-optics splitter configured tosplit a laser beam emitted from the laser source into an object beam anda reference beam, a modulator, a second fiber-optics splitter configuredto split the object beam, a third fiber-optics splitter configured tosplit the reference beam, a plurality of fiber-optics circulators, aplurality of fiber-optics re-combiners, and a plurality of receiversconfigured for receiving signals from the plurality of fiber-opticsre-combiners; a multi-channel receiver array; and a computer having adisplay, a multi-channel digitizer, and a microprocessor configured fordigital signal processing and data analysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, the conformal beam illuminationscheme has a plurality of dynamically reconfigurable conformalilluminating probes, a single mode (SM) fiber array, a collimatingarray, a Faraday rotator, a steerable micro-electro-mechanical-system(MEMS) mirror array, and an objective lens; a multi-channelinterferometer, wherein the multi-channel interferometer is amulti-channel heterodyne interferometer, wherein the multi-channelheterodyne interferometer is an all-fiber multi-channel heterodyneinterferometer having a laser source, an optical isolator, a firstfiber-optics splitter configured to split a laser beam emitted from thelaser source into an object beam and a reference beam, a modulator, asecond fiber-optics splitter configured to split the object beam, athird fiber-optics splitter configured to split the reference beam, aplurality of fiber-optics circulators, a plurality of fiber-opticsre-combiners, and a plurality of receivers configured for receivingsignals from the plurality of fiber-optics re-combiners; a multi-channelreceiver array; and a computer having a display, a multi-channeldigitizer, and a microprocessor configured for digital signal processingand data analysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a fiber array, and a plurality of conformalilluminating probes; a multi-channel interferometer, wherein themulti-channel interferometer is a multi-channel heterodyneinterferometer, wherein the multi-channel heterodyne interferometer is ahybrid fiber-bulk optic multi-channel heterodyne interferometer having alaser source, a fiber-optics splitter configured to split a laser beamemitted from the laser source into an object beam and a reference beam,a modulator, at least one collimating telescope configured forcollimating the object beam, at least one collimating telescopeconfigured for collimating the reference beam, at least one polarizingbeam splitter, at least one non-polarizing beam splitter, a plurality ofcollimating arrays, and a plurality of receivers; a multi-channelreceiver array; and a computer having a display, a multi-channeldigitizer, and a microprocessor configured for digital signal processingand data analysis. Additionally, at least one conformal illuminatingprobe has a terminal end with (a) a bare fiber angle polished to anyangle from 8 degrees to 45 degrees, (b) a mirrored right-anglemicro-prism, or (c) a microlens.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a polarizing maintaining (PD) fiber array, a fiber ferrule, aflat-field lens, and a quarter-waveplate; a multi-channelinterferometer, wherein the multi-channel interferometer is amulti-channel heterodyne interferometer, wherein the multi-channelheterodyne interferometer is a hybrid fiber-bulk optic multi-channelheterodyne interferometer having a laser source, a fiber-optics splitterconfigured to split a laser beam emitted from the laser source into anobject beam and a reference beam, a modulator, at least one collimatingtelescope configured for collimating the object beam, at least onecollimating telescope configured for collimating the reference beam, atleast one polarizing beam splitter, at least one non-polarizing beamsplitter, a plurality of collimating arrays, and a plurality ofreceivers; a multi-channel receiver array; and a computer having adisplay, a multi-channel digitizer, and a microprocessor configured fordigital signal processing and data analysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a single mode (SM) fiber array, a fiber ferrule, a flat-fieldlens, and a Faraday rotator; a multi-channel interferometer, wherein themulti-channel interferometer is a multi-channel heterodyneinterferometer, wherein the multi-channel heterodyne interferometer is ahybrid fiber-bulk optic multi-channel heterodyne interferometer having alaser source, a fiber-optics splitter configured to split a laser beamemitted from the laser source into an object beam and a reference beam,a modulator, at least one collimating telescope configured forcollimating the object beam, at least one collimating telescopeconfigured for collimating the reference beam, at least one polarizingbeam splitter, at least one non-polarizing beam splitter, a plurality ofcollimating arrays, and a plurality of receivers; a multi-channelreceiver array; and a computer having a display, a multi-channeldigitizer, and a microprocessor configured for digital signal processingand data analysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a fiber array, and a plurality of conformalilluminating probes; a multi-channel interferometer, wherein themulti-channel interferometer is a multi-channel homodyne interferometer;a multi-channel receiver array; and a computer having a display, amulti-channel digitizer, and a microprocessor configured for digitalsignal processing and data analysis. Additionally, at least oneconformal illuminating probe has a terminal end with (a) a bare fiberangle polished to any angle from 8 degrees to 45 degrees, (b) a mirroredright-angle micro-prism, or (c) a microlens.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a polarizing maintaining (PD) fiber array, a fiber ferrule, aflat-field lens, and a quarter-waveplate; a multi-channelinterferometer, wherein the multi-channel interferometer is amulti-channel homodyne interferometer; a multi-channel receiver array;and a computer having a display, a multi-channel digitizer, and amicroprocessor configured for digital signal processing and dataanalysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a single mode (SM) fiber array, a fiber ferrule, a flat-fieldlens, and a Faraday rotator; a multi-channel interferometer, wherein themulti-channel interferometer is a multi-channel heterodyneinterferometer, a multi-channel interferometer, wherein themulti-channel interferometer is a multi-channel homodyne interferometer;a multi-channel receiver array; and a computer having a display, amulti-channel digitizer, and a microprocessor configured for digitalsignal processing and data analysis.

Another exemplary embodiment of the present invention's system forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry, the conformal beam illuminationscheme has a plurality of dynamically reconfigurable conformalilluminating probes, a single mode (SM) fiber array, a collimatingarray, a Faraday rotator, a steerable micro-electro-mechanical-system(MEMS) mirror array, and an objective lens; a multi-channelinterferometer, wherein the multi-channel interferometer is amulti-channel homodyne interferometer; a multi-channel receiver array;and a computer having a display, a multi-channel digitizer, and amicroprocessor configured for digital signal processing and dataanalysis.

An exemplary embodiment of the present invention's method for conformalimaging vibrometry capable of real-time measurements of the dynamicmotions of any arbitrary two-dimensional or three-dimensional structurecomprises the steps of setting a suitable conformal beam illuminationscheme based on a geometry of a test object; setting a plurality ofobject beams from a multi-channel interferometer with the determinedconformal beam illumination scheme; setting each object beam in adirection that conforms to a local normal axis of a surface of the testobject; illuminating the test object using the plurality of objectbeams; and executing a simultaneous multi-point measurement of the testobject, wherein the simultaneous multi-point measurement includes atleast a measurement of real-time, dynamic motions of the test object.

Another exemplary embodiment of the present invention's method forconformal imaging vibrometry capable of real-time measurements of thedynamic motions of any arbitrary two-dimensional or three-dimensionalstructure comprises the steps of setting a suitable conformal beamillumination scheme based on a geometry of a test object; setting aplurality of object beams from a multi-channel interferometer with thedetermined conformal beam illumination scheme; setting each object beamin a direction that conforms to a local normal axis of a surface of thetest object; illuminating the test object using the plurality of objectbeams; executing a simultaneous multi-point measurement of the testobject, wherein the simultaneous multi-point measurement includes atleast a measurement of real-time, dynamic motions of the test object;and demodulating the simultaneous multi-point measurements using amicroprocessor configured for digital signal processing and dataanalysis.

An exemplary embodiment of the present invention's method for conformalimaging vibrometry capable of real-time measurements of the dynamicmotions of any arbitrary two-dimensional or three-dimensional structureemploying operational modal analysis (OMA) comprises the steps ofsetting at least one suitable conformal beam illumination scheme basedon a geometry of a test object in its natural operating environment;setting a plurality of object beams from a multi-channel interferometerwith at least one determined conformal beam illumination scheme; settingeach object beam in a direction that conforms to a local normal axis ofa surface of the test object; illuminating the test object using theplurality of object beams; executing a simultaneous multi-pointmeasurement of structural responses of the test object; and performingoperational modal analysis on the multi-point measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

Other systems, methods, features and advantages of the present inventionwill be or will become apparent to one of ordinary skill in the art uponexamination of the following figures and detailed descriptions. It isintended that all such additional apparatuses, systems, methods,features and advantages be included within this description, be withinthe scope of the present invention, and be protected by the appendedclaims. Component parts shown in the drawings are not necessarily toscale, and may be exaggerated to better illustrate the importantfeatures of the present invention. In the drawings, like referencenumerals designate like parts throughout the different views, wherein:

FIG. 1A is a schematic depicting an exemplary embodiment of the presentinvention's system for conformal imaging vibrometry capable of real-timemeasurements of the dynamic motions of any arbitrary two-dimensional orthree-dimensional structure.

FIG. 1B is a schematic depicting an exemplary embodiment of the presentinvention's multi-channel interferometer for conformal imagingvibrometry capable of real-time measurements of the dynamic motions ofany arbitrary two-dimensional or three-dimensional structure.

FIG. 1C is a schematic depicting an exemplary embodiment of the presentinvention's conformal beam illumination scheme and in particular, aradial two-dimensional conformal array.

FIG. 1D is a schematic depicting different exemplary embodiments of theterminal ends of the present invention's conformal illuminating probes.

FIG. 2 is a schematic depicting another exemplary embodiment of thepresent invention's multi-channel interferometer for conformal imagingvibrometry capable of real-time measurements of the dynamic motions ofany arbitrary two-dimensional or three-dimensional structure.

FIG. 3 is a schematic depicting an exemplary embodiment of the presentinvention's conformal beam illumination scheme and, in particular, aplanar conformal array with free space projection employing apolarization maintaining (PM) two-dimensional (2D) fiber array.

FIG. 4 is a schematic depicting another exemplary embodiment of thepresent invention's conformal beam illumination scheme and, inparticular, a planar conformal array with free space projectionemploying a single mode (SM) fiber array.

FIG. 5 is a schematic depicting another embodiment of the presentinvention's conformal beam illumination scheme and, in particular, adynamically reconfigurable conformal beam illumination withtwo-dimensional (2D) MEMS mirror.

FIG. 6 is a flowchart depicting an exemplary embodiment of the presentinvention's method for conformal imaging vibrometry capable of real-timemeasurements of the dynamic motions of any arbitrary two-dimensional orthree-dimensional structure.

FIG. 7 is a flowchart depicting another exemplary embodiment of thepresent invention's method for conformal imaging vibrometry capable ofreal-time measurements of the dynamic motions of any arbitrarytwo-dimensional or three-dimensional structure.

FIG. 8 shows experimental data in which the present invention's CIV,system 100, was configured to support dynamic imaging of real-timestructural behavior of micro vibratory resonators.

DETAILED DESCRIPTION

FIG. 1A is a schematic depicting an exemplary embodiment of the presentinvention's system for conformal imaging vibrometry capable of real-timemeasurements of the dynamic motions of any arbitrary two-dimensional orthree-dimensional structure. The present invention's system represents asubstantial departure from conventional bulk-optic vibrometer designsbecause it supports multi-channel configurations without significantimpact on system size or complexity. The present invention's systemachieves this outcome by incorporating fiber-optics component technologyfrom the telecommunications field as part of an all-digital,multi-channel implementation of the traditional single-channelheterodyne vibrometer. Specifically, the present invention's systemincorporates fiber-optics architecture from the laser source input tothe receiver coupling scheme. The present invention's system uses activeand passive fiber-optics components throughout to guarantee a robustoptical alignment. The exemplary embodiment of FIG. 1A captures thesenovel features of the present invention's system.

In the exemplary embodiment of the present invention's system in FIG.1A, system 100 has a multi-channel interferometer 117, conformal beamillumination scheme 119, a multi-channel receiver array 112, and acomputer 113 having (i) a multi-channel digitizer for digitizing thesignals received from multi-channel receiver array 112, (ii) amicroprocessor for digital signal processing and data analysis of theconformal imaging vibrometry, and (iii) a computer display.Multi-channel interferometer 117 has a laser source 101, an opticalisolater 102, a first fiber-optics splitter 103, a modulator 104, asecond fiber-optics splitter 105 a, a third fiber-optics splitter 105 b,fiber-optics circulators 106 a-106 g, fiber-optics re-combiners 110a-110 g, and receivers 111 a-111 g. FIG. 1B shows multi-channelinterferometer 117 apart from system 100 on FIG. 1A.

Multi-channel interferometer 117 can be a multi-channel heterodyneinterferometer or a multi-channel homodyne interferometer. Amulti-channel heterodyne interferometer can incorporate integratedfiber-optics component technology originally developed for thetelecommunications field at 1550-nm but re-purposed in support ofmulti-channel parallel sensor designs or can employ active and passivesingle mode (SM) or polarization maintaining (PM) fiber-opticscomponents at any wavelength. Use of a linearly polarized laser and PMfiber components throughout the interferometer offers a direct means ofmaintaining polarization alignment along the fiber optic interferometer.SM fiber components in conjunction with suitable variable polarizationcontrollers can be also employed to align the polarization in thereference and object arms.

Additionally, multi-channel interferometer 117 can also be an all-fibermulti-channel interferometer, an all-bulk optic multi-channelinterferometer, or a hybrid fiber-bulk optic interferometer. In theexemplary embodiment of FIG. 1A, multi-channel interferometer 117 is anall-fiber multi-channel heterodyne interferometer and in particular,multi-channel interferometer 117 is an all-fiber multi-channelheterodyne Mach-Zehnder interferometer. Multi-channel interferometer 117has an all-fiber optic architecture extending from laser source 101 tothe plurality of receivers 111 a-111 g.

Laser source 101 emits laser beam 118, which feeds into optical isolator102 and subsequently into first fiber-optics splitter 103. Laser source101 can be a narrow linewidth fiber laser. First fiber-optics splitter103 can be a 1×2 fiber-optics splitter configured to split laser beam118 into an object beam 114 and a reference beam 115. In this exemplaryembodiment of FIG. 1, fiber-optics splitter 103 splits laser beam 118into 80-90% object beam 114 and 10-20% reference beam 115. Thefiber-optics splitter 103 can split beam 118 in any desired ratio.

Modulator 104 offsets the frequency of reference beam 115 required forFM carrier generation. Modulator 104 can be a highly compact andelectronically efficient lithium-niobate waveguide phase modulator. In alithium-niobate waveguide phase modulator, the reference beam is phasemodulated by a serrodyne voltage ramp applied to the electrodes of thisphase modulator. Alternatively, modulator 104 can be a serialconfiguration of two acousto-optic modulators, such as Bragg cells, plusdual radiofrequency (RF) drivers. Modulator 104 can also be any otheroptical fiber phase modulator capable of implementing a heterodynecarrier modulation scheme.

Second fiber-optics splitter 105 a splits object beam 114 according to adesired number of channels. Similarly, third fiber-optics splitter 105 bsplits reference beam 115 according to a desired number of channels. Thefiber-optics splitters 105 a-105 b can each be a 1×N fiber-opticssplitter, wherein N can be 2, 4, 8, 16, 32 or any other integer in whichthe incident beam, either object beam 114 or reference beam 115, can bedivided into by the 1×N fiber-optics splitter. In the exemplaryembodiment of FIG. 1, fiber-optics splitters 105 a-105 b are each a 1×8channel fiber-optics splitter. Thus, as shown in FIG. 1, secondfiber-optics splitter 105 a splits object beam 114 into 8 channels, andthird fiber-optics splitter 105 b splits reference beam 115 into 8channels.

Multi-channel interferometer 117 can employ amplitude divisionmultiplexing or wavelength division multiplexing. In the exemplaryembodiment of FIG. 1, multi-channel interferometer 117 employs amplitudedivision multiplexing. As shown in FIG. 1, multi-channel interferometer117 has a 1×8 channel fiber-optics splitting network. The multi-channelinterferometer 117 can have a 1×N channel fiber-optics splitting networkdepending on the desired number of channels. The desired number ofchannels employed by fiber-optics splitters 105 a-105 b should beconsistent with that of the multi-channel fiber-optics splitting network116.

Fiber-optics circulators 106 a-106 g deliver the respective sub-dividedobject beams to conformal beam illumination scheme 119. Conformal beamillumination scheme 119 is a two-dimensional radial conformal array.Conformal beam illumination scheme 119 has a fiber array 116, aplurality of conformal illuminating probes 108 a-108 g, and test object109. Fiber array 116 has object beams delivered from a multi-channelinterferometer, such as multi-channel interferometer 117 or 200. Fiberarray 116 can be a single mode (SM) fiber array or a polarizingmaintaining (PD) fiber array. Thus, in the exemplary embodiment of FIG.1A, fiber-optics circulators 106 a-106 g deliver the respectivesub-divided object beams to conformal illuminating probes 108 a-108 g.FIG. 1C shows conformal beam illumination scheme 119 apart from system100 on FIG. 1A.

Test object 109 can be any structure having an arbitrary geometry. Thus,depending on the particular geometry of test object 109, conformalilluminating probes 108 a-108 g can be radial, circular, cylindrical, orspherical conformal illuminating probes. In the exemplary embodiment ofFIGS. 1A and 1C, test object 109 is a wineglass micro-resonator andthus, conformal illuminating probes 108 a-108 g are radial conformalilluminating probes. As shown in FIG. 1, conformal illuminating probes108 a-108 g are arranged radially around test object 109. Each conformalilluminating probe 108 a-108 g illuminates the respective sub-dividedobject beam on a single point on test object 109.

This arrangement of conformal illuminating probes 108 a-108 g, as shownin FIG. 1, is an exemplary embodiment of the present invention'sconformal beam illumination scheme 119. However, the arrangement ofconformal illuminating probes 108 a-108 g can be tailored to thespecific structural geometry of interest (i.e., planar, circular,cylindrical, spherical or an arbitrary curved/warped 2D or 3D surface).Thus, system 100 allows for a two-dimensional or three-dimensionaltesting of test objects that are small structures with rapidly varyingsurface curvatures, such as a micro-resonator (i.e., MEMS resonator).

For the purpose of characterization, test object 109 is illuminated withmultiple laser beams from conformal illuminating probes 108 a-108 gwhose directions conform to the local normal axis of the surface. Thisapproach enables high-speed vibration imaging of whole-body dynamics ofarbitrarily shaped structures in real-time, with no multiplexed datacapture or synthesized motion reconstruction, as is currently practiced.By measuring test object 109's vibrations simultaneously at multiplepoints, system 100 is able to reproduce the structural behavior underoperational conditions, which can then be spectrally decomposed todetermine the modal, complex modal and transient nature of the truestructural dynamics.

The speed at which these measurements can be made permits a wide rangeof further characterization tests. For example, the effect of pressureand temperature variations on the object's dynamics can be studied inreal-time, where previously these parameters had to be held or assumedconstant throughout the measurement process. In this exemplaryembodiment of FIG. 1, system 100 uses heterodyne interferometry (i.e.multi-channel interferometer 117), in which the velocity of thevibrating surface is encoded in the Doppler sidebands of a frequencymodulated carrier. The microprocessor, such as the microprocessor incomputer 113, recovers the displacement (or velocity) data bydemodulating the measured, digitized signals to yield the local surfacedisplacement (or velocity) time histories, while the full data setprovides an animated display of the real-time surface deformation (orvelocity) of the sample under transient (or, in fact, arbitrary)stimulus. In addition to general application, system 100 is uniquelyapplicable to the capture of short-lived, chaotic or transient surfacemovement or other vibrations which are not currently amenable to studyby the current state of the art.

Conformal illuminating probes 108 a-108 g can be electrically passive aslaser source 101 can be linked by a fiber optic feed through anumbilical to the probe station, while optical signals scattered backfrom the surface of test object 109 could be fiber guided from conformalilluminating probes 108 a-108 g back to multi-channel receiver array112.

Optical signals scattered back from the surface of test object 109 arere-coupled back into the respective conformal illuminating probes 108a-108 g, and subsequently carried back to multi-channel interferometer117. Each fiber re-combiner 110 a-110 g combines the reflected lightwith the respective modulated output from the respective reference beam.In the exemplary embodiment of FIG. 1, fiber re-combiners 110 a-110 gare each a 2×1 3-dB fiber re-combiner. The fiber re-combiners 110 a-110g can each be of any desired split ratio.

Receivers 111 a-111 g each receives its respective re-combined outputsfrom its respective fiber re-combiner 110 a-110 g. Receivers 111 a-111 gcan be pigtailed photodiodes. The output signals from receivers 111a-111 g are fed to a series of trans-impedance amplifiers andsubsequently sent to multi-channel receiver array 112 where these outputsignals are digitized. Multi-channel receiver array 112 can be amulti-channel digital receiver array.

The outputs from multi-channel receiver array 112 comprise the signalsof the heterodyne carrier and contain sideband modulation signalsassociated with the object vibrations. These outputs are transferred tocomputer 113 having (i) a multi-channel digitizer for digitizing thesignals received from multi-channel receiver array 112, (ii) amicroprocessor for digital signal processing and data analysis of theconformal imaging vibrometry, and (iii) a computer display. Recovery ofthe baseband displacements or velocities of the test structure at eachof the illuminated points is performed in software by, for example,digital I and Q (in-phase and quadrature) demodulation, but maysimilarly employ a variety of other heterodyne demodulation methods. Thebaseband velocity-time data for each point in the conformal array can bereplayed by computer 113. Further time and frequency domain analysis maybe employed to reveal specific aspects of the object dynamics such asmodal coalescence, splitting, damping and environmental sensitivities.

FIG. 1B is a schematic depicting an exemplary embodiment of the presentinvention's multi-channel interferometer for conformal imagingvibrometry capable of real-time measurements of the dynamic motions ofany arbitrary two-dimensional or three-dimensional structure. As shownin FIG. 1B, an exemplary embodiment of the present invention'smulti-channel interferometer is multi-channel interferometer 117. FIG.1B shows multi-channel interferometer 117 apart from system 100 of FIG.1A. Multi-channel interferometer 117 can connect with conformal beamillumination schemes 119, 300, 400, or 500.

FIG. 1C is a schematic depicting an exemplary embodiment of the presentinvention's conformal beam illumination scheme and, in particular, aradial two-dimensional conformal array. As shown in FIG. 1C, anexemplary embodiment of the present invention's conformal beamillumination scheme is conformal beam illumination scheme 119. FIG. 1Cshows conformal beam illumination scheme 119 apart from system 100 ofFIG. 1A. Conformal beam illumination scheme 119 can connect withmulti-channel interferometers 117 or 200.

FIG. 1D is a schematic depicting different exemplary embodiments of theterminal ends of the present invention's conformal illuminating probes,such as the terminal ends of conformal illuminating probes 108 a-108 g.The respective terminal ends of conformal illuminating probes 108 a-108g terminate the respective probe fibers, such as probe fibers 120. Eachprobe fiber 120 illuminates a test object, such as test object 109.Thus, the present invention discloses different ways in which probefibers 120 can illuminate test object 109 through the use of differentterminal ends of conformal illuminating probes 108 a-108 g.

FIG. 1D discloses three different exemplary embodiments of the terminalends of conformal illuminating probes 108 a-108 g. In the firstexemplary embodiment on FIG. 1D, a terminal end of a conformalilluminating probe has a bare fiber angle polished to approximately 8degrees, as shown by identifier 121 on FIG. 1D. As a result, probe fiber120 is terminated in a manner that minimizes the return loss from thefiber end face. The bare fiber angle can be polished to any angleranging from 8 degrees to 45 degrees.

In the second exemplary embodiment on FIG. 1D, a terminal end of aconformal illuminating probe has a mirrored right-angle micro-prism,which includes a right-angle micro-prism 122 and a mirrored hypotenuse123. As a result, probe fiber 120 is terminated in a manner thatlaunches the output beam at right angles to the axis of the fiber.

In the third exemplary embodiment on FIG. 1D, a terminal end of aconformal illuminating probe has a micro-lens 124. As a result, probefiber 120 is terminated in a manner that collimates or focuses the lightemitted from the fiber end.

FIG. 2 is a schematic depicting another exemplary embodiment of thepresent invention's multi-channel interferometer for conformal imagingvibrometry capable of real-time measurements of the dynamic motions ofany arbitrary two-dimensional or three-dimensional structure.Multi-channel interferometer 200 can be implemented into the exemplaryembodiment of the present invention's system in FIG. 1A by replacingmulti-channel interferometer 117 in FIG. 1A. In the exemplary embodimentof FIG. 2, multi-channel interferometer 200 is a hybrid fiber-bulk opticmulti-channel heterodyne interferometer, such as a hybrid fiber-bulkoptic multi-channel Mach-Zehnder heterodyne interferometer. As a hybridfiber-bulk optic multi-channel heterodyne interferometer, multi-channelinterferometer 200 has a fiber optic architecture extending between (a)laser source 201 and modulator 203, and (b) receivers 211-212 andmulti-channel digitizer 112.

Multi-channel interferometer 200 has a laser source 201, a fiber-opticssplitter 202, a modulator 203, collimating telescopes 204 and 207, apolarizing beam splitter 205, a non-polarizing beam splitter 208,collimating arrays 206, 209, and 210, and receivers 211 and 212.

Laser source 201 emits laser beam 214. Like laser source 101, lasersource 201 can be a narrow linewidth fiber laser. Laser source 101, 201and the fiber-optics components can be implemented at any visible laserwavelengths, such as 532-nm or 633-nm or near-infrared and infraredlaser wavelengths such as 800-nm, 1060-nm, 1300-nm or 1550-nm. However,system operation at 1550-nm has important advantages because (i) a widevariety of fiber optic components at this wavelength can be adapted fromthe telecommunication field and are commercially available,off-the-shelf items, (ii) Class 1 eye safe designation permits the useof higher optical power to enhance the return reflected signal and,therefore, the sensitivity and the signal to noise of the system, (iii)smaller detection bandwidths for a given vibration frequency andamplitude, and (iv) availability of compact semiconductor or fiberlasers providing high power and narrow line-width.

Fiber-optics splitter 202 splits laser beam 214 into an object beam 215and a reference beam 216. Fiber-optics splitter 202 can be a 1×2fiber-optics splitter. The fiber-optics splitter 202 can be of any splitratio.

Modulator 203 offsets the frequency of reference beam 216 required forFM carrier generation. Modulator 203 can be a waveguide phase modulator.Modulator 203 can be a highly compact and electronically efficientlithium-niobate waveguide phase modulator. In a lithium-niobatewaveguide phase modulator, the reference beam is phase modulated by aserrodyne voltage ramp applied to the electrodes of this phasemodulator. Alternatively, modulator 203 can be a serial configuration oftwo acousto-optic modulators, such as Bragg cells, plus dualradiofrequency (RF) drivers. Modulator 203 can also be any other opticalfiber phase modulator capable of implementing a heterodyne carriermodulation scheme.

Collimating telescope 204 collimates object beam 215. Collimated objectbeam 215 is then transmitted to polarizing beam splitter 205.Collimating telescope 207 collimates reference beam 216. Collimatedreference beam 216 is then transmitted to non-polarizing splitter 208.Collimating telescopes 204 and 207 can be fiber pigtailed collimatingtelescopes.

Object beam 215 from polarizing beam splitter 205 illuminatescollimating microlens array 206. Polarizing beam splitter 205 can be apolarizing beam splitting cube. Collimating array 206 can be acollimating microlens array which is aligned to a two-dimensional (2D)fiber array. With microlens fill-factors approaching 98%, object beam215 is efficiently coupled into the multiple channels of theinterferometer array. Object beam 215 is then guided to the conformalilluminating probes, such as conformal illuminating probes 108 a-108 h.In FIG. 2, identifier 213 represents the connections to the respectiveconformal illuminating probes 108 a-108 h.

Non-polarizing beam splitter 208 splits reference beam 216 into twocollimated reference beams, each of which couple to its respectivecollimating arrays 209 and 210. Collimating arrays 209 and 210 can eachbe a collimating microlens array which is aligned to a two-dimensional(2D) fiber array. Non-polarizing beam splitter 208 can be anon-polarizing beam splitting cube.

Optical signals scattered back from the surface of a test object, suchas test object 109, are re-coupled back into the respective conformalilluminating probes 108 a-108 g, and subsequently carried back tomulti-channel interferometer 200. Collimating array 206 collimates thesereturned optical signals and subsequently mixes in each fiber of thearray with the respective coupled phase modulated reference light.

The mixed signals are then fiber guided to a distributed receiver array,such as receivers 211 and 212, where the analog outputs are subsequentlydigitized and demodulated using standard FM or similar schemes torecover the baseband velocities from the carrier signals. Receivers 211and 212 can be photo-receivers. This dual receiver array constitutes abalanced detection scheme which improves signal to noise by cancellingcommon mode effects such as relative intensity noise (RN) while doublingthe amplitude of the baseband signal. Where balanced detection is notcritical, a single receiver array may be employed at the expense of 3 dBoptical losses suffered at the unused output port.

The output signals from receivers 211 and 212 are fed to a series oftrans-impedance amplifiers and subsequently sent to a multi-channelreceiver array, such as multi-channel receiver array 112 of FIG. 1A. Theoutputs from multi-channel receiver array 112 comprise the signals ofthe heterodyne carrier and contain sideband modulation signalsassociated with the object vibrations. These outputs are transferred tocomputer 113 having (i) a multi-channel digitizer for digitizing thesignals received from multi-channel receiver array 112, (ii) amicroprocessor for digital signal processing and data analysis of theconformal imaging vibrometry, and (iii) a computer display. Recovery ofthe baseband displacements or velocities of the test structure at eachof the illuminated points is performed in software by, for example,digital I and Q (in-phase and quadrature) demodulation, but maysimilarly employ a variety of other heterodyne demodulation methods. Thebaseband velocity-time data for each point in the conformal array can bereplayed by computer 113. Further time and frequency domain analysis maybe employed to reveal specific aspects of the object dynamics such asmodal coalescence, splitting, damping and environmental sensitivities.

FIG. 3 is a schematic depicting an exemplary embodiment of the presentinvention's conformal beam illumination scheme. A conformal beamillumination scheme employs diffractive optical elements or spatiallight modulators followed by free-space projection optics to focus theoutput beams on a distant object. Such embodiments are suited to planarconformal illumination schemes where the object of interest issubstantially planar (or moderately curved) over the illuminated area.Exemplary embodiments of such planar conformal beam illumination schemesare conformal beam illumination schemes 300 and 400, as detailed inFIGS. 3-4. Conformal beam illumination schemes 300 and 400 can becombined with multi-channel interferometers 117 and 200. Conformal beamillumination scheme 119 of FIGS. 1A and 1C is an exemplary embodiment ofa radial conformal beam illumination scheme.

In FIG. 3, conformal beam illumination scheme 300 is a planar conformalarray with free space projection employing a polarization maintaining(PM) two-dimensional (2D) fiber array. Conformal beam illuminationsscheme 300 has fiber array 301, a fiber ferrule 302, a flat-field lens303, a quarter waveplate 304, and object coverage 305. Fiber array 301is a PM 2D fiber array having object beams from planar conformalilluminating probes connected to multi-channel interferometer 117 or200. Next, the object beams from fiber array 301 terminate into fiberferrule 302. Fiber ferrule 302 can be a two-dimensional (2D) fiberferrule.

Next, the object beams from fiber ferrule 302 are imaged by flat-fieldlens 303. Flat-field lens 303 can be an F-theta lens whose magnificationis determined according to the desired working distance and objectcoverage. After the object beams pass through flat-field lens 303,quarter waveplate 304 is employed so that the incident ‘s’ polarizationis returned in the orthogonal ‘p’ mode whereupon it is reflected by, forexample, polarizing beam splitter 205 of FIG. 2 towards receivers 211and 212 of FIG. 2. After quarter waveplate 304, the object beams focuson object coverage 305. The reflected light from object coverage 305passes through the aforementioned elements and back to the multi-channelinterferometer, such as multi-channel interferometer 117 or 200.

FIG. 4 is a schematic depicting another exemplary embodiment of thepresent invention's conformal beam illumination scheme. In FIG. 4,conformal beam illumination scheme 400 is a planar conformal array withfree space projection employing a single mode (SM) fiber array.Conformal beam illuminations scheme 400 has a fiber array 401, a fiberferrule 402, a Faraday rotator 403, a flat-field lens 404, and objectcoverage 405. Fiber array 401 is an SM fiber array having object beamsdelivered from multi-channel interferometer 117 or 200. Next, the objectbeams from fiber array 401 terminate into fiber ferrule 402. Fiberferrule 402 can be a two-dimensional (2D) fiber ferrule. Next, theobject beams from fiber ferrule 402 pass through Faraday rotator 403,and subsequently are imaged by flat-field lens 404. Flat-field lens 404can be an F-theta lens whose magnification is determined according tothe desired working distance and object coverage. After flat-field lens404, the object beams focus on object coverage 405.

The reflected light from object coverage 405 passes through theaforementioned elements and back to the multi-channel interferometer,such as multi-channel interferometer 117 or 200. In particular, thereflected light from object coverage 405 passes through Faraday rotator403 returning in the orthogonal polarization mode whereupon thepolarization drifts which are common in SM fiber are exactly reversed onreturn. The emergent linear orthogonal polarized light is then similarlyreflected by, for example, polarizing beam splitter 205 of FIG. 2towards receivers 211 and 212 of FIG. 2.

FIGS. 1-4 present exemplary embodiments of the present invention'ssystems, multi-channel interferometers, and conformal beam illuminationschemes for conformal imaging vibrometry capable of real-timemeasurements of the dynamic motions of any arbitrary two-dimensional orthree-dimensional structure. The application of the present inventionmay in practice range from real-time characterization of micro-scaleMEMS resonators up to limit cycle oscillations associated with wing tipflutter. Thus, as discussed, different configurations of these exemplaryembodiments can be achieved by different combinations of (a) differentmulti-channel interferometers, such as multi-channel interferometers 117and 200, with (b) different conformal beam illumination schemes, such asconformal beam illumination schemes 300 and 400. The preferredconfiguration depends on the particular structure of the test object.For small structures with rapidly varying surface curvatures, a staticfiber array may be employed as in FIGS. 1A-1C where a fixed fiberadapter (in the illustrated case, radial) is employed to conform thefiber array to the surface geometry. In the case of convoluted surfaceshapes, the static fiber adapter may be fabricated by surface moldingtechniques to conform closely to the desired geometry. For both largeand small structures with modest curvature over the area of interest,the planar conformal probe may be employed with or without projectionoptics, respectively. Any of these applications may employ multi-channelinterferometers 117 and 200 according to channel density requirementswhere the scheme of FIG. 2 or variations thereof may be more readilyextended to high channel counts (hundreds) in a relatively compactformat.

FIG. 5 is a schematic depicting another exemplary embodiment of thepresent invention's conformal beam illumination scheme. In FIG. 5,conformal beam illumination scheme 500 is a dynamically reconfigurableconformal illumination with a two-dimensional (2D) MEMS mirror.Conformal beam illumination scheme 500 can be combined with theexemplary embodiments of FIGS. 1-2, such as system 100 and multi-channelinterferometers 117 and 200.

Conformal beam illumination scheme 500 provides a greater degree offlexibility than the fixed or static configurations of conformal beamillumination schemes 119, 300, and 400. For example, fiber opticswitches have been developed for high density telecommunications channelmultiplexing. As shown in FIG. 5, these switches employ high densityfiber optic collimating arrays, such as collimating array 501, in orderto switch the signal from any given output channel to any arbitrarychannel of a matched collimating fiber input array. The beam steeringelement in fiber optic switches typically comprises an array of atwo-dimensional (2D) steerable (XY) MEMS mirrors, such as micro mirrorarray 503, which can be independently controlled.

Conformal beam illumination scheme 500 has a fiber array 506,collimating array 501, a Faraday rotator 502, a micro mirror array 503,an objective lens 504, and a convoluted object surface 505. Fiber array506 can be a SM fiber array having object beams delivered frommulti-channel interferometer 117 or 200. Next, the object beams fromfiber array 506 terminate into collimating array 501. Collimating array501 can be a two-dimensional (2D) fiber ferrule with matched microlensarray. Next, the object beams from collimating array 501 pass throughFaraday rotator 502 and subsequently, illuminate micro mirror array 503.Micro mirror array 503 can be a two-dimensional (2D) steerable (XY) MEMSmicro mirror array. Micro mirror array 503 is then used to independentlysteer the object beams into a conformal illuminating pattern which isthen projected and focused onto convoluted object surface 405 comprisingpositive and negative curvatures by objective lens 504 such that theincident beams are everywhere normal to the surface. The ability torapidly configure micro mirror array 503 for different or even variablestructural profiles might further employ additional surface profilingcapability using a variety of structured lighting methods.

Conformal beam illumination scheme 500 may also readily be employed toprovide an extremely versatile reconfigurable beam pattern configuredaccording to the shape of the test object with the measurement beampattern and density varied according to specific areas of interest. Theoutput pattern can therefore be switched from two-dimensional (2D)square, rectangular, linear, circular or concentric circular accordingto the exact shape of the test object which may include inclusions orvoids for which the return signal might otherwise be lost. For shortworking distances or with the aid of additional optics, the angles ofincidence for any group of three (3) marginal channels may be sufficientto direct three (3) beams to any single point of coincidence in order torecover the full surface velocity vector (out-of plane (Z) and in-plane(X&Y)).

FIG. 6 is a flowchart depicting an exemplary embodiment of the presentinvention's method for conformal imaging vibrometry capable of real-timemeasurements of the dynamic motions of any arbitrary two-dimensional orthree-dimensional structure. This present invention's method, such asmethod 600, provides the ability to fully characterize the dynamicbehavior of an object of any arbitrary geometry, deploying a laser beamarray tailored to the specific structural geometry of interest, such asplanar, circular, cylindrical, spherical or an arbitrary curved/warpedtwo-dimension (2D) surface or three-dimensional (3D) surface.

As shown in FIG. 6, method 600 comprises steps 601 to 605. At step 601,a suitable conformal beam illumination scheme is selected based on ageometry of a test object. Various exemplary embodiments of the presentinvention's conformal beam illumination schemes have been disclosed,such as conformal beam illumination schemes 119, 300, 400, and 500. Ifthe geometry of the test object is substantially planar, or moderatelycurved, then a planar conformal beam illumination scheme is suitable. Anexample of such test object would be a large or a small structure withmodest curvature over the area of interest. Conformal beam illuminationschemes 300 and 400 of FIGS. 3-4 are exemplary embodiments of thepresent invention's planar conformal beam illumination schemes.

If the geometry of the test object is not substantially planar, or notmoderately curved, then a conformal beam illumination scheme issuitable. An example of such test object would be a small structure withrapidly varying surface curvatures. Conformal beam illumination scheme119 of FIG. 1C is an exemplary embodiment of the present invention'sradial conformal beam illumination scheme. Additionally, if the testobject has convoluted surface shapes, a static fiber adapter may befabricated by surface molding techniques to conform closely to thedesired geometry. Conformal beam illumination schemes 119, 300, and 400are exemplary embodiments of fixed or static configurations.

If the test object has a greater degree of varying curvature, then aconformal beam illumination scheme permitting a greater degree offlexibility than a fixed or static configuration is suitable, such as adynamically reconfigurable conformal beam illumination scheme. Conformalbeam illumination scheme 500 is an exemplary embodiment of the presentinvention's dynamically reconfigurable conformal beam illumination withtwo-dimensional (2D) MEMS mirror.

At step 602, a plurality of object beams from a multi-channelinterferometer are set in accordance with the selected conformal beamillumination scheme. Depending on the selected conformal beamillumination scheme, the plurality of object beams can be configured fordiverging, converging or collimated illumination. Multi-channelinterferometers 117 and 200 are exemplary embodiments of theinterferometers deployed in the present invention's system. If conformalbeam illumination scheme 119 is selected, then conformal illuminatingprobes 108 a-108 g can be arranged radially around the test object suchthat each object beam from each probe will illuminate a different pointon the test object, as shown in FIG. 1C. As previously articulated,conformal illuminating probes 108 a-108 g can be radial, circular,cylindrical, or spherical conformal illuminating probes depending on thegeometry of the test object. If either of conformal beam illuminationschemes 300 or 400 is selected, then object beams from radial conformalilluminating probes are arranged as shown in FIGS. 3-4. If conformalbeam illumination scheme 500 is selected, then object beams fromdynamically reconfigurable conformal illuminating probes are arranged asshown in FIG. 5.

At step 603, each object beam is set in a direction that conforms to alocal normal axis of a surface of the test object. By way of example, ifconformal beam illumination scheme 119 is selected, then conformalilluminating probes 108 a-108 g are arranged so that the direction ofthe respective object beams from the probes conform to the local normalaxis of the surface at the respective point on the test object. Thisapproach enables high-speed vibration imaging of whole-body dynamics ofarbitrarily shaped structures in real-time, with no multiplexed datacapture or synthesized motion reconstruction, as is currently practiced.

At step 604, the test object is illuminated by the plurality of objectbeams. By way of example, if conformal beam illumination scheme 119 isselected, then the plurality of object beams from conformal illuminatingprobes 108 a-108 g illuminate the test object radially, as shown in FIG.1C. Laser source 101 provides the illumination source for the pluralityof object beams from conformal illuminating probes 108 a-108 g.

At step 605, executing a simultaneous multi-point measurement of thetest object, wherein the simultaneous multi-point measurement includesat least a measurement of real-time, dynamic motions of the test object.Additionally, in an alternative embodiment, the simultaneous multi-pointmeasurement further includes measurements of the test object'sdisplacement, velocity, vibration, and acceleration in a steady-state, ashort-lived state, a non-periodic state, a chaotic state, a transientstate, or any combinations thereof. Additionally, the simultaneousmulti-point measurements can be dispersed in sufficient number to fullyspatially image surface deformations and vibrations of the test object.

By measuring test object 109's vibrations simultaneously at multiplepoints, system 100 is able to reproduce the structural behavior underoperational conditions, which can then be spectrally decomposed todetermine the modal, complex modal and transient nature of the truestructural dynamics. The speed at which these measurements can be madepermits a wide range of further characterization tests. For example, theeffect of pressure and temperature variations on the object's dynamicscan be studied in real-time, where previously these parameters had to beheld or assumed constant throughout the measurement process. In thisexemplary embodiment of FIG. 1, system 100 uses heterodyneinterferometry (i.e. multi-channel interferometer 117), in which thevelocity of the vibrating surface is encoded in the Doppler sidebands ofa frequency modulated carrier. The microprocessor, such as themicroprocessor in computer 113, recovers the displacement (or velocity)data by demodulating the measured, digitized signals to yield the localsurface displacement (or velocity) time histories, while the full dataset provides an animated display of the real-time surface deformation(or velocity) of the sample under transient (or, in fact, arbitrary)stimulus. In addition to general application, system 100 is uniquelyapplicable to the capture of short-lived, chaotic or transient surfacemovement or other vibrations which are not currently amenable to studyby the current state-of-the-art.

Similar benefits and capabilities might accrue from integration of othermethods to dynamically manipulate and individually reposition themeasurement fibers on a case-by-case basis to accommodate differentdiameter structures and/or different structural geometries.Accommodating variable configurations would require, for example, thatthe manipulator have the ability to translate the measurement probestoward or away from the test surface and to incline the measurementfibers at any desired angle.

FIG. 7 is a flowchart depicting another exemplary embodiment of thepresent invention's method for conformal imaging vibrometry capable ofreal-time measurements of the dynamic motions of any arbitrarytwo-dimensional or three-dimensional structure using operational modalanalysis (OMA). Such method is depicted as method 700 in FIG. 7. OMA isalso known as output-only modal analysis. A comparatively recent fieldof study concerns the method of QMA, wherein vibration measurements areperformed directly on structures in their natural (operating)environment. The application of traditional modal analyses under suchconditions is generally prohibited because of difficulties associatedwith accurately measuring the input-forcing functions. In their naturalenvironment, the input stimuli may come from multiple sources andinclude combinations of steady state, broadband and transient sources.The method of operational modal analyses sometimes referred to as outputonly modal analysis has been developed to analyze the modal behaviorstructures in the normal operating environment. OMA assumes that theinput-forcing functions are not known, or cannot be measured, andinstead measures the structural response (outputs) at multiple locationssimultaneously, typically using accelerometer arrays. The disclosedconformal imaging vibrometer, such as system 100 of FIG. 1, offers anon-contact alternative for the application of OMA on structures whosedynamics may be affected by the additional load associated withsurface-mounted accelerometers. For more general application of OMA, theconformal imaging vibrometer, such as system 100 of FIG. 1, offers rapidacquisition of multi-point vibration spectra, providing the basis for anoptical (non-contact) implementation of operational modal analysis inaddition to the practical benefit of avoiding lengthy preparationsinvolved in mounting and removing accelerometer arrays.

As shown in FIG. 7, method 700 comprises steps 701 to 705. At step 701,a suitable conformal beam illumination scheme is selected based on ageometry of a test object in its natural environment. Various exemplaryembodiments of the present invention's conformal beam illuminationschemes have been disclosed, such as conformal beam illumination schemes119, 300, 400, and 500. If the geometry of the test object issubstantially planar, or moderately curved, then a planar conformal beamillumination scheme is suitable. An example of such test object would bea large or a small structure with modest curvature over the area ofinterest. Conformal beam illumination schemes 300 and 400 of FIGS. 3-4are exemplary embodiments of the present invention's planar conformalbeam illumination schemes.

If the geometry of the test object is not substantially planar, or notmoderately curved, then a conformal beam illumination scheme issuitable. An example of such test object would be a small structure withrapidly varying surface curvatures. Conformal beam illumination scheme119 of FIG. 1C is an exemplary embodiment of the present invention'sradial conformal beam illumination scheme. Additionally, if the testobject has convoluted surface shapes, a static fiber adapter may befabricated by surface molding techniques to conform closely to thedesired geometry. Conformal beam illumination schemes 119, 300, and 400are exemplary embodiments of a fixed or static configuration.

If the test object has a greater degree of varying curvature, then aconformal beam illumination scheme permitting a greater degree offlexibility than a fixed or static configuration is suitable, such as adynamically reconfigurable conformal beam illumination scheme. Conformalbeam illumination scheme 500 is an exemplary embodiment of the presentinvention's dynamically reconfigurable conformal beam illumination withtwo-dimensional (2D) MEMS mirror.

At step 702, a plurality of object beams from a multi-channelinterferometer are set in accordance with the selected conformal beamillumination scheme. Multi-channel interferometers 117 and 200 areexemplary embodiments of the interferometers deployed in the presentinvention's system. If conformal beam illumination scheme 119 isselected, then conformal illuminating probes 108 a-108 g are arrangedradially around the test object such that each object beam from eachprobe will illuminate a different point on the test object, as shown inFIG. 1C. If either conformal beam illumination scheme 300 or 400 isselected, then object beams from planar conformal illuminating probesare arranged as shown in FIGS. 3-4. If conformal beam illuminationscheme 500 is selected, then object beams from dynamicallyreconfigurable conformal illuminating probes are arranged as shown inFIG. 5.

At step 703, each object beam is set in a direction that conforms to alocal normal axis of a surface of the test object. By way of example, ifconformal beam illumination scheme 119 is selected, then conformalilluminating probes 108 a-108 g are arranged so that the direction ofthe respective object beams from the probes conforms to the local normalaxis of the surface at the respective point on the test object. Thisapproach enables high-speed vibration imaging of whole-body dynamics ofarbitrarily-shaped structures in real-time, with no multiplexed datacapture or synthesized motion reconstruction, as is currently practiced.

At step 704, the test object is illuminated by the plurality of objectbeams. By way of example, if conformal beam illumination scheme 119 isselected, then the plurality of object beams from conformal illuminatingprobes 108 a-108 g illuminates the test object radially, as shown inFIG. 1. Laser source 101 provides the illumination source for theplurality of object beams from conformal illuminating probes 108 a-108g.

At step 705, executing a simultaneous multi-point measurement ofstructural responses of the test object, wherein the simultaneousmulti-point measurement includes at least a measurement of real-time,dynamic motions of the test object. Additionally, in an alternativeembodiment, the simultaneous multi-point measurement further includesmeasurements of the test object's displacement, velocity, vibration, andacceleration in a steady-state, a short-lived state, a non-periodicstate, a chaotic state, a transient state, or any combinations thereof.Additionally, the simultaneous multi-point measurements can be dispersedin sufficient number to fully spatially image surface deformations andvibrations of the test object.

At step 706, an operational modal analysis is performed on themulti-point measurements.

FIG. 8 shows experimental data in which the present invention's CIV,system 100, was configured to support dynamic imaging of real-timestructural behavior of micro vibratory resonators. System 100 wasemployed to measure the spatio-temporal dynamics of a 5-mm diameterwineglass micro-resonator test object. As shown in FIG. 1C, conformalilluminating probes 108 a-108 h were arranged in the close proximity ofthe micro-resonator test object such as the diverging beams exciting thePM fibers (numerical aperture=0.12) were approximately normally incidentto the test surface, allowing the measurement of the out-of-plane motionin the equatorial plane of the micro-resonator. The particularmicro-resonator geometry requires a radial conformal array for whichpurpose eight measuring PM fiber probes were aligned at 45 degreeintervals along the equatorial line of the micro-resonator, as depictedin FIG. 1C. As previously discussed, conformal illuminating probes 108a-108 h generate an array of eight laser spots on the vibrating testdevice while the scattered light from each of the measurement points iscollected back in the PM fibers probes and mixed with the referencesignal at the receiver.

The substrate of the test object was mounted on a piezo electric ceramicdisc transducer vibrating in radial mode (a 7 mm diameter×0.5 mmthickness disc). Individual split modes were selectively excited attheir corresponding frequencies and the time-displacement (or velocity)distributions were simultaneously recovered at the eight illuminatingpoints. The microprocessor of computer 113 displays the data to show thereal-time energy flow around the micro-resonator for any given set ofdrive conditions. The out-of-plane spatial displacement/velocity timehistories are then spline fitted and represented as an animated “movie”that shows the dynamic behavior of the vibrating structure in real time(but reviewed in slow motion).

FIG. 8 represents a single frame of the animated display illustratingthe displacement profiles of n=2 non-degenerate mode at maximumdisplacement during one cycle. The displacements are shown withdifferent scaling factors between the modes for better representation.As expected, the principal axes of elasticity for the split n=2 mode areseparated by 45 degrees. The data provides not a qualitative “image,”but a quantitative diagnostic map of the entire structural velocity,whose complete temporal evolution is contained in the entire capturedsequence. In addition to providing dynamic time-domain surface vibrationprofiles, the data may be analyzed in a frequency domain in order tofurther characterize the dynamic spatial modal content of the structuralvibrations (resonant modes, high harmonics modes, frequency split) or intime domain to determine Q factor and damping axis.

The highly localized passive measurement based on fiber delivery of theoptical beam employed in the all-fiber CIV lends itself naturally tovacuum integration. The down-link fibers of the CIV were, accordingly,integrated via a vacuum feed-through port into a vacuum chamber. As thefull spatio-temporal nature of the micro device dynamic can be measuredin vacuum, CIV is anticipated to serve as a valuable tool in tailoringgyro structural design, electrode placement, and signal drive schemes inorder to optimize device performance.

Exemplary embodiments of the invention have been disclosed in anillustrative style. Accordingly, the terminology employed throughoutshould be read in a non-limiting manner. Although minor modifications tothe teachings herein will occur to those well versed in the art, itshall be understood that what is intended to be circumscribed within thescope of the patent warranted hereon are all such embodiments thatreasonably fall within the scope of the advancement to the art herebycontributed, and that that scope shall not be restricted.

What is claimed is:
 1. A system for conformal imaging vibrometry,comprising: a conformal beam illumination scheme configured forconformal imaging vibrometry of real-time dynamic behavior of astructure having an arbitrary geometry; a multi-channel interferometer;a multi-channel receiver array; and a computer having a multi-channeldigitizer, a microprocessor configured for digital signal processing anddata analysis, and a display.
 2. The system of claim 1, wherein themulti-channel interferometer is a multi-channel heterodyneinterferometer.
 3. The system of claim 2, wherein the multi-channelheterodyne interferometer is an all-fiber multi-channel heterodyneinterferometer having a laser source, an optical isolator, a firstfiber-optics splitter configured to split a laser beam emitted from thelaser source into an object beam and a reference beam, a modulator, asecond fiber-optics splitter configured to split the object beam,wherein the second fiber-optics splitter is a 1-by-N channelfiber-optics splitter, wherein N is any positive integer greater than 2,a third fiber-optics splitter configured to split the reference beam,wherein the third fiber-optics splitter is a 1-by-N channel fiber-opticssplitter, wherein N is any positive integer greater than 2, a pluralityof fiber-optics circulators, a plurality of fiber-optics re-combiners,and a plurality of receivers configured for receiving signals from theplurality of fiber-optics re-combiners.
 4. The system of claim 3,wherein the conformal beam illumination scheme has a fiber array and aplurality of conformal illuminating probes.
 5. The system of claim 4,wherein at least one conformal illuminating probe has a terminal endwith a bare fiber angle polished to any angle from 8 degrees to 45degrees.
 6. The system of claim 4, wherein at least one conformalilluminating probe has a terminal end with a mirrored right-anglemicro-prism.
 7. The system of claim 4, wherein at least one conformalilluminating probe has a terminal end with a microlens.
 8. The system ofclaim 3, wherein the conformal beam illumination scheme has a pluralityof planar conformal illuminating probes, a polarizing maintaining (PD)fiber array, a fiber ferrule, a flat-field lens, and aquarter-waveplate.
 9. The system of claim 3, wherein the conformal beamillumination scheme has a plurality of planar conformal illuminatingprobes, a single mode (SM) fiber array, a fiber ferrule, a flat-fieldlens, and a Faraday rotator.
 10. The system of claim 3, wherein theconformal beam illumination scheme has a plurality of dynamicallyreconfigurable conformal illuminating probes, a single mode (SM) fiberarray, a collimating array, a Faraday rotator, a steerablemicro-electro-mechanical-system (MEMS) mirror array, and an objectivelens.
 11. The system of claim 2, wherein the multi-channel heterodyneinterferometer is a hybrid fiber-bulk optic multi-channel heterodyneinterferometer having a laser source, a fiber-optics splitter configuredto split a laser beam emitted from the laser source into an object beamand a reference beam, a modulator, at least one collimating telescopeconfigured for collimating the object beam, at least one collimatingtelescope configured for collimating the reference beam, at least onepolarizing beam splitter, at least one non-polarizing beam splitter, aplurality of collimating arrays, and a plurality of receivers.
 12. Thesystem of claim 11, wherein the conformal beam illumination scheme has afiber array, and a plurality of conformal illuminating probes.
 13. Thesystem of claim 12, wherein at least one conformal illuminating probehas a terminal end with a bare fiber angle polished to any angle from 8degrees to 45 degrees.
 14. The system of claim 12, wherein at least oneconformal illuminating probe has a terminal end with a mirroredright-angle micro-prism.
 15. The system of claim 12, wherein at leastone conformal illuminating probe has a terminal end with a microlens.16. The system of claim 11, wherein the conformal beam illuminationscheme has a plurality of planar conformal illuminating probes, apolarizing maintaining (PD) fiber array, a fiber ferrule, a flat-fieldlens, and a quarter-waveplate.
 17. The system of claim 11, wherein theconformal beam illumination scheme has a plurality of planar conformalilluminating probes, a single mode (SM) fiber array, a fiber ferrule, aflat-field lens, and a Faraday rotator.
 18. The system of claim 11,wherein the conformal beam illumination scheme has a plurality ofdynamically reconfigurable conformal illuminating probes, a single mode(SM) fiber array, a collimating array, a Faraday rotator, a steerablemicro-electro-mechanical-system (MEMS) mirror array, and an objectivelens.
 19. The system of claim 1, wherein the multi-channelinterferometer is a multi-channel homodyne interferometer.
 20. A methodfor conformal imaging vibrometry, comprising the steps of: setting asuitable conformal beam illumination scheme based on a geometry of atest object; setting a plurality of object beams from a multi-channelinterferometer with the determined conformal beam illumination scheme;setting each object beam in a direction that conforms to a local normalaxis of a surface of the test object; illuminating the test object usingthe plurality of object beams; and executing a simultaneous multi-pointmeasurement of the test object, wherein the simultaneous multi-pointmeasurement includes at least a measurement of real-time, dynamicmotions of the test object.
 21. The method of claim 20, wherein at thestep of executing the simultaneous multi-point measurement of the testobject, the simultaneous multi-point measurements are dispersed insufficient number to fully spatially image surface deformations andvibrations of the test object.
 22. The method of claim 20, wherein atthe step of executing the simultaneous multi-point measurement of thetest object, the simultaneous multi-point measurement further includesmeasurements of the test object's displacement, velocity, vibration, andacceleration in a steady-state, a short-lived state, a non-periodicstate, a chaotic state, a transient state, or any combinations thereof.23. The method of claim 20, further comprising the step of: demodulatingthe simultaneous multi-point measurements using a microprocessorconfigured for digital signal processing and data analysis.
 24. Themethod of claim 20, wherein at the step of setting a plurality of objectbeams from the multi-channel interferometer with the determinedconformal beam illumination scheme, the plurality of object beams areconfigured for diverging illumination.
 25. The method of claim 20,wherein at the step of setting a plurality of object beams from themulti-channel interferometer with the determined conformal beamillumination scheme, the plurality of object beams are configured forconverging illumination.
 26. The method of claim 20, wherein at the stepof setting a plurality of object beams from the multi-channelinterferometer with the determined conformal beam illumination scheme,the plurality of object beams are configured for collimatedillumination.